en holm



(No Model.)

T. WALLACE & O. A. EN HOLM,

MICROPHONE.

No. 353,337. Patented Nov. 30, 1886.

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UNITED STATES PATENT OFFICE.

THOMAS WALLACE AND OSCAR A. EN HOLM, on NEW YORK, N. Y.

MICROPHONE.

SPECIFICATION Iorming part of Letters Patent No. 353,337, dated November30, 1886.

Application filed January 26, 1886. Serial No. 183,844. i (No model.) i

To all whom, it may concern.-

Be it known that we, THOMAS WALLACE and OSCAR A. EN HOLM, citizens ofthe United States, and residents of the city, county, and State of NewYork, have invented certain new and useful Improvements in Microphones,of which the following is a specification.

Our invention relates to microphones, and has for its object to improvethe construction of such instruments and to render them cheap, simple,and effective, and at thesame time more delicate and of greatercapacity, with the least liability of getting out of adjustment; and tothese ends our invention consists in a microphone constructedsubstantially as hereinafter pointed out.

Referring to the accompanying drawings, forming part of thisspecification, for a more particular description, Figure l is a planview of one form of a microphone embodying our invention. Fig. 2 is aside view of the same. Fig. 3 is a cross-section of Fig. 1. Figs. 4 and5 are modified forms.

Many attempts have heretofore been made to construct microphones thatshall be effective and practical; but they have been subject to more orless objections, either in regard to delicacy of operation under allconditions or ex pense of manufacture.

Our object has been to construct a microphone that is simple and cheap,and not liable to get out of order, and at the same time be capable oftransmitting all kinds of sounds, from the faintest whisper to theloudest talking, without mutilating the sounds and without adjustment ofthe parts.

In carrying out our invention any sort of a can or box may be used tosupport the working parts, and we have shown in the drawings theselatter parts only, as they can be applied to the case in any well-knownmanner.

We use a diaphragm, A, of any suitable material, without regard to itsstructure or thickness, as we have found that any kind will work, from athin sheet of paper-board to a thick piece of wood. Upon this diaphragmwe mount a bridge-piece, B, of any suitable non-conducting materialsuchas wood, rub ber, or the like-and this bridge-piece is tapered at oneend, as b, and this end is secured.

to the edge of the diaphragm, while the other end rests upon afoot-piece, b which is secured to the center of the diaphragm. Thebridgepiece may be conveniently secured in this position by glue,mucilage, &c., and is preferably made in one piece. The face of thebridge is grooved at c c, to receive the bars of carbon or electrodes 0O, which may be secured in any manner, as by glue. These bars 0 G areeach connected to one end of the line-wire L L, one portion of whichgoes to the distant station, while the other is connected to the ground,or in any other usual way, the battery being interposed directly'in theline at any desired locality. The terminals of the linewire areconnected to the ends of these pieces 0 O by solder or by being wrappedaround the end, or any other equivalent manner that will give goodelectric contact. Upon these bars is placed a bar, D, which restsloosely thereon, and is suspended by a fine cord from the pin or screwcl, or held. up by means of a supporting pin. This bar or electrode isweighted at its lower end, as at D, byboringthe same audinserting someheavy metal, as lead. The bar D thus rests lightly upon the bars 0 C,and forms the connecting-link between the latter, so that the electriccurrent flows from one of the bars 0 to the bar D, and from this to theother bar 0, and in this manner we obtain a very delicate but continuouscontact between the electrodes, the weighted end of the bar D preventingit from being thrown out of contact by any sound-vibrations, no matterof what character. These bars or electrodes are made of the best hardcarbon, (and we prefer what is known as Carris carbon,) and theirsurfaces are highly polished, so that they pre sent to each other agreat number of very fine points of contact, and as the vibrations ofthe diaphragm under the in tluence of sound-waves are imparted to them,there is a very delicate variation of each and all of these finecontacts, and the electric current is therefore varied'to a greatdegree. I

In order to properly protect the carbon bars from extraneous substancesthat might interfere with their operation or their high condi* tion ofpolish, we provide a cover, E, which may be of paper or the like, andwhich we se- \Ve are aware that carbon bars secured directly on thediaphragm and having a carbon bar or ball resting on them, and also thathalfdisk carbons secured on a bridge fastened to the central portionofthediaphragm and adiskcarbon suspended to rest on the saidhalf-disks,have been used in microphones; but our i11- vention is distinguishedfrom such constructions, in that the suspended baris weighted andresting on and between the carbon bars on the bridge, and is much lessliable to be thrown out of contact by the vibration of the diaphragm,

and the bridge has one end connected at or near the edge of thediaphragni,while the elevated end is at the center thereof, thusincreasing the susceptibility of the microphone to slight vibrations.

Having now described our invention, what we claim isl. The combination,with the diaphragm, of

the bridgepiece secured thereto, the bars' secured to the bridge-pieceand connected to the line, and the suspended and weighted bar resting onand between said bars, substantially as described.

2. The combination, with the diaphragm and the bridge-piece carrying thecarbon bars, of a covering connected to the bridge-piece and extendingover the bars, substantially as described. I

3. The combination, with the diaphragm, of the bridge-piece, theelevated end of which bears upon the center of the diaphragm and theother is secured at or near the edge of the carbon bars carried by thebridge-piece, and the weighted bar resting upon and between the fixedbars, substantially as described.

In testimony whereof we have signed our names to this specification inthe presence of two subscribing witnesses.

THOMAS WVALLAOE. OSCAR A. EN HOLM.

